The present invention relates to a displacement type compressor which deals with a refrigerant, air, carbon dioxide and the other compression gases, and is particularly preferable for a displacement type compressor which is driven by a self-start synchronous motor which starts as an induction motor and performs synchronous operation by performing synchronization pull-in almost at a synchronous rotational frequency.
As one of motors having high energy efficiency, there is a self-start synchronous motor. In displacement type compressors represented by a scroll compressor, a screw compressor, a reciprocating compressor, a rotary compressor and the like, it becomes necessary to improve energy efficiency of a driving motor to improve its energy efficiency, and research and development of the displacement type compressor having the high energy efficiency using the self-start synchronous motor are made increasingly.
As a prior art relating to a displacement type compressor using a self-start synchronous motor, there is a refrigerating apparatus shown in JP-A-2003-35289. The refrigerating apparatus disclosed in JP-A-2003-35289 includes a compressor which is driven by a self-start synchronous motor, a condenser and an evaporator. The self-start synchronous motor is provided with a winding wire which is wound around an iron core of its rotor so as to operate as an induction-motor, and a permanent magnet which is magnetized to the iron core of the rotor in the same way so as to operate as a synchronous motor, and is driven as an induction motor at startup and as a synchronous motor at a time of steady state operation. A refrigerant gas is compressed in a compression chamber which is constructed by a fixed scroll and a rotary scroll, and is discharged through the inside of a compression container out of the compressor. The refrigerating apparatus is provided with a bypass circuit which establishes a bypass between a discharge side and an inlet side of the compressor so as to bypass the discharge side and the inlet side before starting.
Also, as a prior art relating to a displacement type compressor using a self-start synchronous motor, there is an air-conditioner shown in JP-A-2001-3863. The air conditioner disclosed in JP-A-2001-3863 includes a refrigeration cycle connecting a compressor, a condenser, a throttle device and an evaporator via a refrigerant pipe. The compressor includes a permanent-magnet-equipped induction-motor (self-start synchronous motor) which starts as an induction motor at startup, and performs synchronous operation by performing synchronization pull-in almost at a synchronous rotational frequency. The refrigeration cycle includes a start load reducing means which bypasses a refrigerant via a predetermined passage resistance between an inlet side and a discharge side of a refrigerant pipe of the compressor.
Further, as a prior art relating to a displacement type compressor using a self-start synchronous motor, there is a fluid transfer device shown in JP-A-2003-134865. The fluid transfer device disclosed in JP-A-2003-134865 includes a compressor, a synchronous motor which drives the compressor, and a start load reducing means which smoothly starts the synchronous motor. The start load reducing means is provided in a flow passage which establishes a bypass between an inlet side and a discharge side of a fluid pipe of the compressor 1.
In the prior arts disclosed in JP-A-2003-35289, JP-A-2001-3863 and JP-A-2003-134865, it is disclosed to facilitate the start by the self-start synchronous motor by providing the start load reducing means which balances so that the pressure difference between the inlet side and the discharge side of the compressor becomes small, but it is desired to further facilitate the start. Thus, in order to enhance synchronization pull-in ability, it is conceivable to increase a cage shaped inductor placed in the rotor, but it causes the problem of increasing an outside diameter dimension of the compressor since the outside diameter of the rotor is made large. Besides, the start load reducing means disclosed in JP-A-2003-35289, JP-A-2001-3863 and JP-A-2003-134865 has been had the problem of complicating the cycle structure because it is provided between the discharge side pipe outside the compressor and the inlet side pipe outside the compressor.